Direct writing of metal features narrower than 100 nm is accomplished by scanning a focused ion beam over a substrate covered with a thin solid metalorg. film. A metalorg. cluster coordination compd. [Ir4(CO)11Br] [N(C2H5)4] is spun on an oxidized Si wafer from acetone soln. and the resulting layer is irradiated with a focused 20 keV Ga-ion beam. The partially decompd. irradiated film regions show a marked decrease of soly. in acetone. Developing by dissolving the nonirradiated parts of the surface hence leaves narrow lines of partially reacted metalorg. precursor. High temp. treatment of these lines, either in vacuum or in a reactive gas stream, completes the decompn. to quite pure Ir as is confirmed by micro-Auger anal. The lines with room temp. elec. resistivities as low as 400 mW cm were obtained at direct writing speeds of 40 mm s-1 to 0.8 mm s-1, which correspond to ion doses of 3.1 * 1016 ions/cm2 to 1.6 * 1015 ions/cm2, resp. The width of the metal lines decreases with decreasing ion dose in this range from 180 to 90 nm. The adhesion to the substrate increases with increasing ion dose. The thickness of the resulting Ir lines depends mainly on the thickness of the metalorg. precursor layer. The max. possible thickness of the [Ir4(CO)11Br] [N(C2H5)4] layer that can be used depends on the effective penetration depth of the ions in this layer.